Methods and Devices for Determination of Beamforming Information

ABSTRACT

There is presented mechanisms for obtaining information for determining beamforming weights for terminal devices. A method is performed by an RE of an access node. The RE has an interface to an REC of the access node. The method comprises obtaining beamforming information per direction from the REC over the interface. The method comprises transforming the beamforming information per direction to beamforming information per antenna, the beamforming information per antenna representing the beamforming weights. The method comprises applying the beamforming weights.

TECHNICAL FIELD

Embodiments presented herein relate to a method, an RE, a computerprogram, and a computer program product for determining beamformingweights or decoding user data for terminal devices. Embodimentspresented herein further relate to a method, an REC, a computer program,and a computer program product for determining beamforming weights ordecoding user data for terminal devices.

BACKGROUND

In communications systems, there may be a challenge to obtain goodperformance and capacity for a given communications protocol, itsparameters and the physical environment in which the communicationssystem is deployed.

For example, the introduction of digital beamforming antenna systems inaccess nodes, such as radio base stations, etc., could allow multiplesimultaneous narrow beams to be used to provide network access to, andthus server, multiple simultaneous served terminal devices, such as userequipment (UE), etc. However, the current split in the access nodesbetween a radio equipment controller (REC) and a radio equipment (RE) asinterconnected by the Common Public Radio Interface (CPRI) may no longerbe feasible as passing the data for each individual radio chain over theCPRI interface could drive prohibitively high data rates.

In more detail, the bit rate of the current CPRI interface scalesdirectly to the number of independent radio chains in the RE. Whenhaving e.g., a 200 MHz carrier bandwidth and 128 physical antennaelements in the beamforming antenna system, a bit rate of 530 Gbps wouldbe needed for the CPRI interface with currently used sample coding. Afurther potential drawback with CPRI is the extra latency from uplink(UL; from terminal device to access node) sampling to the time the datacan be used in downlink (DL; from access node to terminal device), asany information needs to loop in the REC.

One way to address the above-mentioned issues is to collapse the CPRIbased architecture by removing the CPRI interface and putting thefunctionality of the REC in the RE. This approach has at least twodrawbacks. Firstly, due to faster technological development of the RECcompared to the RE, the technical lifetime of the REC is assumed to beshorter than that of the RE. Replacing the RE is more costly thanreplacing the REC. From this aspect it could thus be beneficial to keepthe functionality of the RE as simple as possible. Secondly, the RECcould be configured to make decisions spanning over multiple REs inorder to make coordinated multi-sector decisions, e.g. when some REsrepresent coverage regions of the access node within the coverageregions of other REs (e.g. a so-called micro cell within a so-calledmacro cell). A collapsed architecture loses this overarchingcoordination possibility.

Hence, there is a need for an improved communication between the REC andthe RE.

SUMMARY

An object of embodiments herein is to provide efficient communicationbetween the REC and the RE.

According to a first aspect there is presented a method for obtaininginformation for determining beamforming weights for terminal devices.The method is performed by an RE of an access node. The RE has aninterface to an REC of the access node. The method comprises obtainingbeamforming information per direction from the REC over the interface.The method comprises transforming the beamforming information perdirection to beamforming information per antenna, the beamforminginformation per antenna representing the beamforming weights. The methodcomprises applying the beamforming weights.

According to a second aspect there is presented an RE of an access nodefor obtaining information for determining beamforming weights forterminal devices. The RE has an interface to an REC of the access nodeand comprises processing circuitry. The processing circuitry isconfigured to cause the RE to obtain beamforming information perdirection from the REC over the interface. The processing circuitry isconfigured to cause the RE to transform the beamforming information perdirection to beamforming information per antenna, the beamforminginformation per antenna representing the beamforming weights. Theprocessing circuitry is configured to cause the RE to apply thebeamforming weights.

According to a third aspect there is presented an RE of an access nodefor obtaining information for determining beamforming weights forterminal devices. The RE has an interface to an REC of the access nodeand comprises processing circuitry and a computer program product. Thecomputer program stores instructions that, when executed by theprocessing circuitry, causes the RE to perform operations, or steps. Theoperations, or steps, cause the RE to obtain beamforming information perdirection from the REC over the interface. The operations, or steps,cause the RE to transform the beamforming information per direction tobeamforming information per antenna, the beamforming information perantenna representing the beamforming weights. The operations, or steps,cause the RE to apply the beamforming weights.

According to a fourth aspect there is presented an RE of an access nodefor obtaining information for determining beamforming weights forterminal devices. The RE has an interface to an REC of the access node.The RE comprises an obtain module configured to obtain beamforminginformation per direction from the REC over the interface. The REcomprises a transform module configured to transform the beamforminginformation per direction to beamforming information per antenna, thebeamforming information per antenna representing the beamformingweights. The RE comprises an apply module configured to apply thebeamforming weights.

According to a fifth aspect there is presented a computer program forobtaining information for determining beamforming weights for terminaldevices. The computer program comprises computer program code which,when run on processing circuitry of an RE, causes the RE to perform amethod according to the first aspect.

According to a sixth aspect there is presented a method for providinginformation for determining beamforming weights for terminal devices.The method is performed by an REC of an access node. The REC has aninterface to an RE of the access node. The method comprises obtainingbeamforming information per antenna, the beamforming information perantenna representing the beamforming weights. The method comprisestransforming the beamforming information per antenna to beamforminginformation per direction. The method comprises providing thebeamforming information per direction to the RE over the interface.

According to a seventh aspect there is presented an REC of an accessnode for providing information for determining beamforming weights forterminal devices. The REC has an interface to an RE of the access nodeand comprises processing circuitry. The processing circuitry isconfigured to cause the REC to obtain beamforming information perantenna, the beamforming information per antenna representing thebeamforming weights. The processing circuitry is configured to cause theREC to transform the beamforming information per antenna to beamforminginformation per direction. The processing circuitry is configured tocause the REC to provide the beamforming information per direction tothe RE over the interface.

According to an eighth aspect there is presented an REC of an accessnode for providing information for determining beamforming weights forterminal devices. The REC has an interface to an RE of the access nodeand comprises processing circuitry and a computer program product. Thecomputer program stores instructions that, when executed by theprocessing circuitry, causes the REC to perform operations, or steps.The operations, or steps, cause the REC to obtain beamforminginformation per antenna, the beamforming information per antennarepresenting the beamforming weights. The operations, or steps, causethe REC to transform the beamforming information per antenna tobeamforming information per direction. The operations, or steps, causethe REC to provide the beamforming information per direction to the REover the interface.

According to a ninth aspect there is presented an REC of an access nodefor providing information for determining beamforming weights forterminal devices. The REC has an interface to an RE of the access node.The REC comprises an obtain module configured to obtain beamforminginformation per antenna, the beamforming information per antennarepresenting the beamforming weights. The REC comprises a transformmodule configured to transform the beamforming information per antennato beamforming information per direction. The REC comprises a providemodule configured to provide the beamforming information per directionto the RE over the interface.

According to a tenth aspect there is presented a computer program forproviding information for determining beamforming weights for terminaldevices. The computer program comprises computer program code which,when run on processing circuitry of an REC, causes the REC to perform amethod according to the sixth aspect.

According to an eleventh aspect there is presented a method fordetermining beamforming weights for terminal devices. The method isperformed by an RE of an access node. The RE has an interface to an RECof the access node. The method comprises obtaining beamforminginformation per antenna from at least one of the terminal devices, thebeamforming information per antenna representing the beamformingweights. The method comprises transforming the beamforming informationper antenna to beamforming information per direction. The methodcomprises providing the beamforming information per direction to the RECover the interface.

According to a twelfth aspect there is presented an RE of an access nodefor determining beamforming weights for terminal devices. The RE has aninterface to an REC of the access node and comprises processingcircuitry. The processing circuitry is configured to cause the RE toobtain beamforming information per antenna from at least one of theterminal devices, the beamforming information per antenna representingthe beamforming weights. The processing circuitry is configured to causethe RE to transform the beamforming information per antenna tobeamforming information per direction. The processing circuitry isconfigured to cause the RE to provide the beamforming information perdirection to the REC over the interface.

According to a thirteenth aspect there is presented an RE of an accessnode for determining beamforming weights for terminal devices. The REhas an interface to an REC of the access node and comprises processingcircuitry and a computer program product. The computer program storesinstructions that, when executed by the processing circuitry, causes theRE to perform operations, or steps. The operations, or steps, cause theRE to obtain beamforming information per antenna from at least one ofthe terminal devices, the beamforming information per antennarepresenting the beamforming weights. The operations, or steps, causethe RE to transform the beamforming information per antenna tobeamforming information per direction. The operations, or steps, causethe RE to provide the beamforming information per direction to the RECover the interface.

According to a fourteenth aspect there is presented an RE of an accessnode for determining beamforming weights for terminal devices. The REhas an interface to an REC of the access node. The RE comprises anobtain module configured to beamforming information per antenna from atleast one of the terminal devices, the beamforming information perantenna representing the beamforming weights. The RE comprises atransform module configured to transform the beamforming information perantenna to beamforming information per direction. The RE comprises aprovide module configured to provide the beamforming information perdirection to the REC over the interface.

According to a fifteenth aspect there is presented a computer programfor determining beamforming weights for terminal devices. The computerprogram comprises computer program code which, when run on processingcircuitry of an RE, causes the RE to perform a method according to theeleventh aspect.

According to a sixteenth aspect there is presented a method forobtaining information for determining beamforming weights for terminaldevices. The method is performed by an REC of an access node. The REChas an interface to an RE of the access node. The method comprisesobtaining beamforming information per direction from the RE over theinterface. The method comprises determining the beamforming weights perdirection based on the beamforming information per direction. The methodcomprises providing the beamforming weights per direction to the RE overthe interface.

According to a seventeenth aspect there is presented an REC of an accessnode for providing information for obtaining information for determiningbeamforming weights for terminal devices. The REC has an interface to anRE of the access node and comprises processing circuitry. The processingcircuitry is configured to cause the REC to obtain beamforminginformation per direction from the RE over the interface. The processingcircuitry is configured to cause the REC to determine the beamformingweights per direction based on the beamforming information perdirection. The processing circuitry is configured to cause the REC toprovide the beamforming weights per direction to the RE over theinterface.

According to a eighteenth aspect there is presented an REC of an accessnode for obtaining information for determining beamforming weights forterminal devices. The REC has an interface to an RE of the access nodeand comprises processing circuitry and a computer program product. Thecomputer program stores instructions that, when executed by theprocessing circuitry, causes the REC to perform operations, or steps.The operations, or steps, cause the REC to obtain beamforminginformation per direction from the RE over the interface. Theoperations, or steps, cause the REC to determine the beamforming weightsper direction based on the beamforming information per direction. Theoperations, or steps, cause the REC to provide the beamforming weightsper direction to the RE over the interface.

According to an nineteenth aspect there is presented an REC of an accessnode for obtaining information for determining beamforming weights forterminal devices. The REC has an interface to an RE of the access node.The REC comprises an obtain module configured to obtain beamforminginformation per direction from the RE over the interface. The RECcomprises a determine module configured to determine the beamformingweights per direction based on the beamforming information perdirection. The REC comprises a provide module configured to provide thebeamforming weights per direction to the RE over the interface.

According to a twentieth aspect there is presented a computer programfor obtaining information for determining beamforming weights forterminal devices. The computer program comprises computer program codewhich, when run on processing circuitry of an REC, causes the REC toperform a method according to the sixteenth aspect.

According to a twenty first aspect there is presented a computer programproduct comprises a computer program according to at least one of thefifth aspect, the tenth aspect, the fifteenth aspect, and the twentiethaspect and a computer readable storage medium on which the computerprogram is stored. The computer readable storage medium could be anon-transitory computer readable storage medium.

Advantageously these methods, these REs, these RECs, and these computerprograms allows for efficient communications between the RE and the RECwhen configuring resources for terminal devices.

Advantageously these methods, these REs, these RECs, and these computerprograms allows for large-scale digital beamforming in the access nodewithout significantly upgrading the data rate of the interface betweenthe RE and the REC.

Other objectives, features and advantages of the enclosed embodimentswill be apparent from the following detailed disclosure, from theattached dependent claims as well as from the drawings.

Generally, all terms used in the claims are to be interpreted accordingto their ordinary meaning in the technical field, unless explicitlydefined otherwise herein. All references to “a/an/the element,apparatus, component, means, step, etc.” are to be interpreted openly asreferring to at least one instance of the element, apparatus, component,means, step, etc., unless explicitly stated otherwise. The steps of anymethod disclosed herein do not have to be performed in the exact orderdisclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventive concept is now described, by way of example, withreference to the accompanying drawings, in which:

FIGS. 1, 2, 3, 4, 5, and 6 are schematic diagrams illustrating an accessnode according to embodiments;

FIG. 7 is a schematic illustration of a time-frequency resource gridaccording to embodiments;

FIG. 8 is a schematic illustration comparing energy in antenna space anddirection space;

FIG. 9 is a schematic illustration of a compression subsystem accordingto an embodiment;

FIGS. 10, 11, 12, and 13 are flowcharts of methods according toembodiments;

FIG. 14 is a schematic diagram showing functional units of an REaccording to an embodiment;

FIG. 15 is a schematic diagram showing functional modules of an REaccording to an embodiment;

FIG. 16 is a schematic diagram showing functional units of an RECaccording to an embodiment;

FIG. 17 is a schematic diagram showing functional modules of an RECaccording to an embodiment; and

FIG. 18 shows one example of a computer program product comprisingcomputer readable means according to an embodiment.

DETAILED DESCRIPTION

The inventive concept will now be described more fully hereinafter withreference to the accompanying drawings, in which certain embodiments ofthe inventive concept are shown. This inventive concept may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided by way of example so that this disclosure will be thorough andcomplete, and will fully convey the scope of the inventive concept tothose skilled in the art. Like numbers refer to like elements throughoutthe description. Any step or feature illustrated by dashed lines shouldbe regarded as optional.

FIG. 1 is a schematic diagram illustrating an access node 100 whereembodiments presented herein can be applied. The access node could be aradio base station such as a radio access network node, base transceiverstation, node B, evolved node B, or access point. As disclosed above,the access node comprises at least one Radio Equipment Controller (REC)300 and at least one Radio Equipment (RE) 200. In the illustrativeexample of FIG. 1 the access node comprises one REC and two REs, wherethe REC has one interface 700 to each of the REs. The REs are configuredto perform DL transmissions to, and UL receptions from, terminal devicesboo in beams 500 by using appropriate beamforming weights at theantennas 400. The beamforming weights define at least the pointingdirection and the width of the beams. How to determine the beamformingweights will be disclosed below.

As defined herein the REC does not send in-phase/quadrature (I/Q)samples per physical radio branch to the RE, but rather multiple-inputmultiple-output (MIMO) streams, i.e., I/Q samples per layer. Accordingto the current CPRI specification, the REC can directly address theantennas in the RE, but in the herein disclosed access node that isconfigured to perform beamforming, the RE performs the functionality ofmapping a MIMO stream to a set of physical antenna elements in order togenerate a wanted beam form. Further, in order to enable efficientsimultaneous multi user beamforming, the Fast Fourier Transform (FFT)and Inverse Fast Fourier Transform (IFFT) functions are performed in theRE. In addition, the execution of the beamforming data planefunctionality is added to the RE. Further, the interface 700 between RECand RE could be a packet-based interface, and hence no longer astreaming interface, sending the (frequency domain) samples to the REsymbol by symbol. This allows for quick and flexible allocation ofresources on the interface to different terminal devices. The REC isconfigured to maintain knowledge about the terminal devices, andschedules the air interface between the access node and the terminaldevices. The RE is configured to act on commands received from the REC.

As an illustrative example, consider a communications system having anair interface with a system bandwidth of 400 MHz and that providessupport for 4 MIMO streams and utilizes access nodes with 64 antennasfor beamforming. Using CPRI interfaces between the REC and the REexposing all 64 antennas for the REC would require approximately 54 CPRIinterfaces of 10 Gbps, since a CPRI interface carries about 480 MHz.Further, an interface using virtual antenna ports would require 4 MIMOstreams of 400 MHz, and would require about 4 CPRI interfaces of 10Gbps, since one 10 Gbps CPRI interface still carries data for about 480MHz. By also moving the modulation DL to the RE, the 4 MIMO streams of400 MHz would require 7 Gbps (assuming 256QAM and 20 LTE 20 MHzcarriers), or one 10 Gbps CPRI interface. A higher bitrate of the CPRIinterface is required in the UL if the whole system bandwidth is used,as demodulation is still performed in the REC.

Consider the REC and RE illustrated in FIG. 2 where the REC and RE areinterconnected via an interface denoted RUI, for Radio Unit Interface.In the DL direction the REC sends unmodulated bits for each terminaldevice. The RE modulates the data, places it on the correct subcarrier(thus performing resource mapping), applies beamforming weights(individual per radio branch) defining e.g. width and/or direction ofthe beams and finally convert it to time domain and transmits it to theterminal devices. FIG. 2 shows 1-8 DL MIMO layers on 128 radio branches.In the UL direction the RE samples the signals for each individual radiobranch, converts it to frequency domain, applies beamforming weights,combines the signals from the different radio branches and sends aselection of the modulated combined signal to the REC for furtherdemodulation. FIG. 2 shows 128 radio branches and 1-16 receive beams.The receive beams weakly relates to UL MIMO branches as the more MIMObranches the more receive beams are needed. Typically, more receivebeams than MIMO branches are required. FIG. 2 also shows beamforming asperformed before de-mapping in the RE. The two stages are interlinked asthe beamforming is performed individually per terminal device. FIG. 2further illustrates User Plane Control (UPC) with its air interfacescheduling and link adaptation placed in the REC.

FIG. 3 shows an embodiment of an REC and an RE similar to those in FIG.2. In FIG. 3 the RE is configured to decode reference symbols such asSounding Reference symbols (SRS) in the UL, to store information of howthe reference symbols are best received (e.g., what beamforming weightsmaximizes the SNR of the reference symbols) and to use this storedinformation when performing beamforming in the DL and UL. In FIG. 3 theRE could thus be regarded as autonomous in this respect. To accomplishthis, the RU needs to maintain a storage of information identifying thebest beam shapes for each terminal device, and be configured to applythat information when the corresponding terminal device is scheduled.This minimizes the communication needed over the interface between theREC and the RE with respect to beamforming, but also hides the channelfor the UPC.

The scheduling and the LA are based on the dimension reduced informationwhile further dimensions are used for the determination of beamformingweights. This is equally applicable for UL and DL. The radio channelshould typically be dispersive to be able to gain from adding moredimensions to the beam calculation.

FIG. 4 shows an embodiment of an REC and an RE similar to those in FIG.2. In FIG. 4 the beamforming control is performed primarily by the UPCin the REC. The RE still receives the reference symbols and determinesinformation of how the reference symbols are best received. Thisinformation is then sent to the REC. The REC uses this information tomake an optimal decision on MIMO streams, link adaptation andcoordinated scheduling with other terminal devices, such as MU-MIMO ornulling.

To make the communication and functionality performed in the UPC genericand not heavy dependent on the actual implementation of the RE (e.g., interms of number of branches, antenna layout, etc.) or operating mode(e.g., power save, faulty branches, etc.), the communications betweenthe REC and the RE regarding beamforming properties is expressed in beamdirection space rather than antenna element space. That is, instead ofpresenting a beam as a set of weights of physical antenna elements thebeam is presented as a combination of a set of predetermined beams. Thisalso allows for a more compressed format for this communication, thussaving bit rate on the interface between the REC and the RE. Forinstance, a linear combination of 3 predetermined beams could beexpressed as 3 times 24 bits (an 8-bit beam number+an 8-bit amplitude+an8-bit phase) rather than 128 times 16 bits (an 8-bit amplitude+an 8-bitphase for each of the 128 physical antenna elements). The transformationfrom the physical antenna element space to the beam direction space isperformed by a Dimensions Reduction entity, and the inversetransformation is performed by a Beam Weight Transformation entity.

The operations as performed by the REC and RE in FIG. 4 could bepreferred when the load of the access node is comparatively high and UPCneeds to determine the channel state for the best decision on linkadaptation.

The operations as performed by the REC and RE in FIG. 4 could bepreferred when MU-MIMO or nulling is used, as the UPC then needs channelstate information for the LA of the combination, and to determine whichusers are suitable for simultaneous scheduling, so called MU-MIMOscheduling. Note that nulling may also be applied between terminaldevices served by different REs, and is therefore impossible to performwithin one autonomous RE (as in FIG. 3).

FIG. 5 illustrates an embodiment of an REC and an RE combining thefunctionality of the REC and RE in the embodiments of FIG. 3 and FIG. 4.In comparison to FIG. 3 and FIG. 4, the embodiment of FIG. 5 comprises achannel state memory, an UL/DL BF coefficient calculation entity (whereBF is short for beamforming), an UL/DL quality calculation entity, anUL/DL SNR calculation entity (where SNR is short for signal to noiseratio), and a CSI feedback function (where CSI is short for ChannelState Information).

The channel state memory is configured to store reference symbols sincethe reference symbols are not sent continuously. The transmission rateof the reference symbols is controlled by the access node, and differentterminal devices could have different transmission rates of thereference symbols to allow for the access node to follow channel statechanges. Although the channel state memory is illustrated as storingdata expressed in the beam space in both the RE and the REC, the REcould instead have the channel state memory storing data expressed inthe physical antenna element space.

The UL/DL BF coefficient calculation entity is configured to determinebeamforming weights based on the channel state memory and possible otherconstraints (such as nulling and MU-MIMO) in the RE.

The UL RX weights calculation entity (where RX is short for reception)is configured to determine beamforming weights for the uplink. The ULbeamforming weight determination can be part of maximum-ratio combining(MRC) in the UL demodulator/equalizer. The UPC will order more beamsthan layers, and then the demodulation will combine these to improve SNRor suppress interferers. In the REC, the determination of beamformingweights could be performed in conjunction with the link adaptationwhereas in the case of beamforming weights determined by the RE, thelink adaptation is done independently.

The UL/DL quality calculation entity is configured to determine aquality estimate in respect of each terminal device subject to MU-MIMOscheduling. This quality estimate should reflect the spatial separationbetween wireless terminals as well as the quality achieved whenco-scheduling wireless terminals on the same time/frequency resource.The quality estimate is based on the information in the channel statememory.

The UL/DL SNR calculation entity is configured to determine thebeamforming weights for each terminal device, and to provide the linkadaptation function with estimates of the resulting SNR for each of theterminal devices being scheduled, including the mutual effect ofco-scheduled terminal devices, so called MU-MIMO scheduling. The UEfeedback (CSI) entity is configured to extract information about thechannel provided by the terminal devices (in the UL data plane).Especially, in the case of FDD, where the reciprocity of the DL and ULof the channel to the terminal device is not perfect, it can bebeneficial for the terminal device to send measurements (e.g., CSI) onthe DL signal back to the access node. The CSI reports are extracted bythe REC and used in the channel state memory and thus being consideredin the determination of the beamforming weights.

In configurations where the bitrate of the interface between the REC andthe RE is low (such as below a threshold), the determination ofbeamforming weights is executed by the RE (as in FIG. 3), otherwise thedetermination is executed by the REC (as in FIG. 4). That is, in case oflimited available capacity of the interface between the REC and the RE,the REC (such as in the UPC) determines that the determination ofbeamforming weights is to be executed by the RE. Cell performance of theaccess node could be maximized by determining the beamforming weights inthe REC for all co-scheduled terminal devices (within the same time andfrequency domain) in order to accomplish best link adaptation andorthogonality. This requires that the RE sends extra information to theREC to allow for such determination, and that the REC sends thedetermined beamforming weights to the RE.

Still further, although the REC sends the determined beamforming weightsto the RE, the RE can determine beamforming weights in parallel and thuscombine these internally determined beamforming weights with thebeamforming weights received from the REC. For access nodes where theinterface between the REC and the RE is constrained but not minimized,the dual loops (as defined by the embodiment in FIG. 5) allow for theaccess node to select some terminal devices which can be handled locallyin the RE, thereby making bitrate of the interface between the REC andthe RE available to handle terminal devices which are eligible toMU-MIMO scheduling, e.g. terminal devices using a streaming service.

Having both loops also allows for efficient beamforming coefficientcompression. If a terminal device is note exposed to constraints fromthe UPC, the beamforming coefficient calculation in the REC will be thesame as performed in the RE, and the REC can send a minimal messagerequesting the RE to use its locally calculated values. In case of heavydimensioning reduction, this may even improve the beamforming gain asthe RE has uncompressed channel estimation data. Correspondingly, ifconstraints have changed any beamforming weights, it can be evaluated ifthe constraints have less bits than the new beamforming weights, and canbe transferred instead.

Further aspects applicable to both the embodiments of the RE and the RECwill now be disclosed with reference to the embodiment of REC and REillustrated in FIG. 6. The description of those entities already havingbeen described with reference to any of FIGS. 2-5 is omitted forbrevity.

A reference symbol extraction entity is configured to extract thereference symbols from the Resource Elements that are provided by the ULOFDM FFT from all antenna ports.

The spatial Discrete Fourier Transform (DFT) entity and the channelestimation entity are configured to collectively provide a quality valuefor the fixed beam directions. The quality value is typically based on afiltering of the reference symbols per involved transmission antennas atthe terminal device or MIMO layer within the resource block or for afiltering of a further processed channel estimate per involvedtransmission antennas at the terminal device or MIMO layer and extractedreference symbols. The beam direction space is provided by processingthe reference symbols from all antennas through the spatial DFT entity.

A Dimension Reduction entity is configured to reduce dimension of databeing inputted to the Dimension Reduction entity. For beamforming weightdetermination performed via the REC, the dimension of which fixed beamdirections to use for the beamforming is reduced in order to limit theprocessing load when calculating the weights and the interface rate fromthe RE to the REC. The dimension reduction is based on the qualityvalues from the Spatial DFT entity and the channel estimation entity.For beamforming weight determination performed internally in the RE,more dimensions can be stored, and thus providing better SNR in case ofSU-MIMO transmission.

A Channel state memory is provided in the REC when beamforming weightdetermination is performed via the REC. For the terminal devices thatare scheduled to be measured, the reference symbol based channelestimates can be sent to the REC and stored in the REC Channel StateMemory. These stored channel estimates can then be used for linkadaption as well as determination of beamforming weights. The content ofthe Channel state memory can be used when the data channel is active andis updated for every new measurement of reference symbols. In additionto this the Channel state memory can also store a covariance matrix forall beam directions that have been measured. Those values can becalculated in the REC. If no MU-MIMO pairing shall be done the beamdirection related information does not need to be stored in the Channelstate memory, which will lower the demand on the interface between theREC and the RE.

A Channel state memory is provided in the RE when beamforming weightdetermination is performed internally in the RE. For the referencesymbols of the terminal devices that are scheduled to be measured, thereference symbol based Channel estimates are stored in the RE ChannelState Memory. These stored channel estimates can be used for determiningbeamforming weights. The content of the Channel state memory can be usedwhen the data channel is active and could be updated for every newmeasurement of reference symbols. If no MU-MIMO pairing is done, if nobeam direction related information is stored in the REC based channelstate memory, and if the covariance matrix will be used, the samecovariance matrix as described in the channel state memory in the RECcan instead be stored in the channel state memory in the RE.

A Source Select entity is configured to select and/or combine thebeamforming weights that either originate from the REC or locally fromthe RE. Even in the case where the channel estimate is sent to the REC,a local copy of the channel estimate can be stored in the RE. In casethe REC will not send beamforming weights, the RE will have to usebeamforming weights as determined internally. This can be due to the RECbeing satisfied with the beamforming weights determined internally orthat the beamforming weights are not received properly by the RE (e.g.,due to a lost message). Further, as will be further disclosed below thelocal stored channel estimates can be used to calculate a defaultsetting of the beamforming weights to which the REC sends differentialinformation, see the compression chapter below. The RE can signal to theREC if it has stored a local copy of the channel estimate. This allowsthe REC to know if such compression is possible. The RE can run out oflocal memory, thus such a signalling is recommended (but not mandated).Also, the REC can explicitly order the RE to store a local copy. Also incase no complete channel estimate is sent to the REC, a reduced channelestimate could be transmitted from the RE to the REC to aid the linkadaptation and rank selection.

FIG. 7 gives an example of a time-frequency resource grid 1700applicable to embodiments disclosed herein. The time-frequency resourcegrid illustrates a possible allocation of resources to terminal devicesin terms of a scheduled entity comprising symbols, where each symbolcorresponds to a Resource Element. Each Resource Element in timecorresponds to one orthogonal frequency-division multiplexing (OFDM)symbol and in frequency corresponds to a subcarrier. One subframecomprises 7 symbols; one subcarrier group comprises 24 subcarriers, onesubcarrier chunk comprises 10 subcarrier groups; and one carriercomprises at least one subcarrier chunk.

According to some aspects there are provided mechanisms for efficientdimensions reduction for expressing beamforming weights and informationrelated to determining the beamforming weights.

Reference is now made to FIG. 10 illustrating methods for determiningbeamforming weights for terminal devices as performed by the RE of theaccess node according to embodiments.

As will be disclosed below, the REC in step S206 provides beamforminginformation per direction to the RE 200 over the interface 700. Hence,the RE 200 is configured to perform step S102:

S102: The RE 200 obtains beamforming information per direction from theREC 300 over the interface 700.

The beamforming information is to be applied not per direction but perantenna. The RE 200 is therefore configured to perform step S106:

S106: The RE 200 transforms the beamforming information per direction tobeamforming information per antenna. The beamforming information perantenna represents the beamforming weights.

The beamforming weights are then applied. Thus, the RE 200 is configuredto perform step S108:

S108: The RE 200 applies the beamforming weights.

Further aspects of determining beamforming weights for terminal devicesas performed by the RE will now be disclosed.

In general terms, the beamforming weights are to be applied at antennas400 of the RE 200.

In some aspects the number of beamforming weights in the direction spaceis smaller than the number of beamforming weights in the antenna space.In this aspect the transformation thus results in an expansion ofdimensionality of the of beamforming information. That is, according toan embodiment the beamforming information per antenna is associated witha first dimensionality, and the beamforming information per direction isassociated with a second dimensionality being smaller than the firstdimensionality.

In some aspects the beamforming information is transmitted between theRE 200 and the REC 300 as linear combinations of predetermined beams.Particularly, according to an embodiment the beamforming information perdirection is obtained as a linear combination of predeterminedbeamforming weights per direction.

There could be different ways to perform the transformation. In someaspects the transformation is achieved based on using a DFT.Particularly, according to an embodiment the beamforming information istransformed using a DFT.

As will be further disclosed below, indices i₀, i₁, . . . could be usedthat appoint which of the fixed beam directions (as defined by thepredetermined beams) to use. Particularly, according to an embodimentthe RE 200 is configured to perform (optional) step S104:

S104: The RE 200 obtains information appointing fixed beam directionsfrom the REC 300 over the interface 100. The beamforming information perdirection is then transformed to the beamforming information per antennaonly for the appointed beam directions.

Reference is now made to FIG. 11 illustrating methods for determiningbeamforming weights for terminal devices as performed by the REC of theaccess node according to embodiments.

In general terms, beamforming information is applied per antenna andbeamforming information is therefore often determined per antenna.Therefore the REC 300 is configured to perform step S202:

S202: The REC 300 obtains beamforming information per antenna. Thebeamforming information per antenna represents the beamforming weights.

Beamforming information per direction could enable more efficienttransmission of the beamforming information to the RE 200 than when thebeamforming information is per antenna. Therefore, the REC 300 isconfigured to perform step S204:

S204: The REC 300 transforms the beamforming information per antenna tobeamforming information per direction.

The beamforming information is to be applied by the RE 200 and istherefore provided to the RE 200. That is, the REC 300 is configured toperform step S206:

S206: The REC 300 provides the beamforming information per direction tothe RE 200 over the interface 100.

Further aspects of determining beamforming weights for terminal devicesas performed by the REC will now be disclosed.

The beamforming information per antenna could be obtained from at leastone of the terminal devices boo.

As disclosed above, in some aspects the number of beamforming weights inthe direction space is smaller than the number of beamforming weights inthe antenna space. That is, the embodiment wherein the beamforminginformation per antenna is associated with a first dimensionality, andwherein the beamforming information per direction is associated with asecond dimensionality being smaller than the first dimensionality isalso applicable for the REC 300.

In some aspects only high quality beamforming information per directionis provided. Particularly, according to an embodiment only thebeamforming information per direction having a signal quality measureabove a threshold is provided to the RE 200 over the interface 700 instep S206. The beamforming information per direction that does notfulfil the requirement defined by the threshold is thus not transmittedover the interface 100, thus enabling a reduction in bitrate incomparison to transmitting all the beamforming information per directionor all the beamforming information per antenna.

As disclosed above, in some aspects the transformation is achieved basedon using a DFT. That is, the embodiment wherein the beamforminginformation is transformed using a DFT is also applicable for the REC300.

As disclosed above, in some aspects indices i₀, i₁, . . . could be usedthat appoint which of the fixed beam directions to use. That is,according to an embodiment the REC 300 is configured to perform(optional) step S208:

S208: The REC 300 provides information to the RE 200 over the interface700 appointing which fixed beam directions to use when transforming thebeamforming information per direction to beamforming information perantenna.

Reference is now made to FIG. 12 illustrating methods determiningbeamforming weights for terminal devices as performed by the RE of theaccess node according to embodiments.

S302: The RE 200 obtains beamforming information per antenna from atleast one of the terminal devices boo. The beamforming information perantenna represents the beamforming weights.

Beamforming information per direction could enable more efficienttransmission of the beamforming information to the REC 300 than when thebeamforming information is per antenna. Therefore, the RE 200 isconfigured to perform step 3204:

S304: The RE 200 transforms the beamforming information per antenna tobeamforming information per direction.

The beamforming information is then provided to the REC 300. That is,the RE 200 is configured to perform step S306:

S306: The RE 200 provides the beamforming information per direction tothe REC 300 over the interface 700.

Further aspects of determining beamforming weights for terminal devicesas performed by the RE will now be disclosed.

As disclosed above, in some aspects the number of beamforming weights inthe direction space is smaller than the number of beamforming weights inthe antenna space. That is, the embodiment wherein the beamforminginformation per antenna is associated with a first dimensionality, andwherein the beamforming information per direction is associated with asecond dimensionality being smaller than the first dimensionality isalso applicable for the RE 200.

As disclosed above, in some aspects only high quality beamforminginformation per direction is provided. That is, the embodiment whereinonly the beamforming information per direction having a signal qualitymeasure above a threshold is provided to the REC 300 over the interface700 is also applicable for the RE 200.

As disclosed above, in some aspects the transformation is achieved basedon using a DFT. That is, the embodiment wherein the beamforminginformation is transformed using a DFT is also applicable for the RE300.

As will be further disclosed below, in some aspects the REC 300 providebeamforming weights per direction to the RE 200 over the interface 700.

Hence, according to an embodiment the RE 200 is configured to perform(optional) step S308:

S308: The RE 200 obtains updated beamforming weights per direction fromthe REC 300 over the interface 700.

The beamforming weights per direction are transformed to beamformingweights per antenna. That is, according to this embodiment the RE 200 isconfigured to perform (optional) step S310:

S310: The RE 200 obtains transforms the updated beamforming weights perdirection to updated beamforming weights per antenna.

The beamforming weights per antenna can then be used by the RE 200.Particularly, according to this embodiment the RE 200 is configured toperform (optional) step S312:

S312: The RE 200 applies the updated beamforming weights per antenna.

The updated beamforming weights could be applied at antennas 400 of theRE 200.

Reference is now made to FIG. 13 illustrating a method for determiningbeamforming weights for terminal devices as performed by the REC of theaccess node according to embodiments.

As disclosed above, the RE 200 in step S306 provides beamforminginformation per direction to the REC 300 over the interface 700.Therefore, the REC 300 is configured to perform step S402:

S402: The REC 300 obtains beamforming information per direction from theRE 200 over the interface 700.

Beamforming weight to be applied at the RE 200 are then determined.Particularly, the REC 300 is configured to perform step S406:

S406: The REC 300 determines the beamforming weights per direction basedon the beamforming information per direction.

The beamforming weights are then provided to the RE 200. Thus, the REC300 is configured to perform step S408:

S408: The REC 300 provides the beamforming weights per direction to theRE 200 over the interface 700.

As disclosed above, in some aspects only high quality beamforminginformation per direction is used. That is, according to an embodimentonly the beamforming information per direction having a signal qualitymeasure above the threshold is used when determining the beamformingweights per direction.

In some aspects the beamforming weights are determined based on the rankof the radio channel, either for multiple users or a single user (whereeach user is defined by a respective terminal device 600). Therefore,according to an embodiment the REC 300 is configured to perform(optional) step S404:

S404: The REC 300 obtains channel rank information from the RE 200 overthe interface 700. The beamforming weights per direction are thendetermined based on the channel rank information.

Particular aspects of efficient dimensions reduction of the beamformingweights when communicating information of the beamforming weights, suchas beamforming information, between the REC 300 and the RE 200 will nowbe disclosed in more detail.

The energy or Signal-to-Noise and Interference Ratio (SNIR) of thesignals is approximately the same for all the individual antennas.However, since the received UL signals (or transmitted DL signals) areassociated with pointing directions due to the beamforming weights, theenergy or SNIR will be unevenly distributed between different pointingdirections. This is illustrated in FIG. 8. At 1800 a is illustratedenergy per antenna and at 1800 b is illustrated energy per direction.The energy or SNIR will be high in pointing directions from the accessnode to the terminal devices and low in other directions. This motivatesbeamforming information per direction to be communicated between the RE200 and the REC 300 in accordance with embodiments disclosed above.

If the majority of the energy is located in a subset of all possiblepointing directions, and signals in other directions contains mostlynoise, it is possible to reduce the dimensionality of the signals toprocess by only selecting the directions with significant energy orSNIR. This motivates the above embodiments wherein the beamforminginformation per antenna is associated with a first dimensionality, andwherein the beamforming information per direction is associated with asecond dimensionality being smaller than the first dimensionality.

In general terms, beam information, such as information relating to thebeamforming weights, can be transmitted between the RE and the REC aslinear combinations of predetermined beams. Hence, in accordance withwhat has been disclosed above, the beamforming information per directioncould be represented by a linear combination of predeterminedbeamforming weights per direction

The UL OFDM FFT in FIG. 6 provides the output of Resource Elements forall antennas with N_(a) antenna elements used for beamforming. TheResource Elements include either data or pre-known Reference Symbols.

By extracting the same Reference Symbol from all N_(a) antennas elementsand perform a transformation, e.g., a DFT, on the thus N_(a) ReferenceSymbols, a transformation to a beam direction space from the antennaspace is done. Each value in the N_(a) long output from the transformprovides information about the quality of the signal in one of the N_(a)fixed beam directions.

All beamforming weight calculation can thereby be made in the beamdirection space to minimize complexity. The beamforming weights can bedetermined based on the rank of the radio channel either for multipleusers or a single user and be determined to limit the influence of ULinterference as well as spreading of interference in the DL. This couldbe accomplished by combining enough of the discrete beam directionsproperly weighted to capture the majority of the energy that will resultin a small throughput loss on network level.

The beamforming weights in the direction space (of size N_(d)) for beamb are given by:

w _(d) ^(b) ,d=i ₀ ,i ₁ , . . . ,i _(N) _(d) ⁻¹

When applying the weights to either the UL or DL digital beamforming,they need to be transformed to the antenna space to handle the ResourceElements with data that also is in the antenna space.

The beamforming weights in the antenna space (of size N_(a)) for beam bare given by:

w _(a) ^(b) ,a=0,1, . . . ,N _(a)−1

If the transformation matrix used for performing the inverse transform(i.e. from the direction space to the antenna space) is denoted F_(ad),then:

w _(a) ^(b)=Σ_(d) F _(ad) w _(d) ^(b)

The number of bits for per physical resource block (PRB) group and beamis N_(a)B_(weight), whilst the number of bits for w_(d) ^(b) per PRBgroup and beam is N_(d)B_(weight).

As disclosed above, in order to reduce the load on the interface 700between the REC 300 and the RE 200 the beamforming weights can betransferred from the REC to the RE in the direction space. The number ofbeamforming weights N_(d) in the direction space is smaller than thenumber of beamforming weights N_(a), in the antenna space. That is, thebeamforming information per antenna is associated with a firstdimensionality, and the beamforming information per direction isassociated with a second dimensionality being smaller than the firstdimensionality.

In addition to the beamforming weights in the direction space theindices i₀, i₁, . . . appointing which of the fixed beam directions touse are also transferred to the beamforming weight transformation block.The number of bits to transmit for the indices per PRB group and beam is≤N_(d)B_(ind).

The beam weight transformation block also include a hardware abstractiontransformation function that hide the radio physical implementation andis capable to handle different configurations of number of antennaelements in the beamforming array antenna and other implementationaspects and states. In more detail, since most of the signal processingcan be performed in the directional space, it will be possible to hidesome hardware properties from the signal processing software. Forexample, this enables identical signal processing software to be usedfor different number of antennas but with the same number of useddimensions in the directional space.

Particular aspects of efficient compression of beamforming weights willnow be disclosed in more detail.

Compression of the beamforming weights could be achieved by applyingdifferent encoding techniques to reduce the channel estimate in the ULdirection and the beamforming weights in the DL direction. For example,the encoding techniques could be based on reducing the resolution ofinformation in a transform domain, and/or sending differentialinformation.

FIG. 9 shows a compression subsystem 1900 according to an embodimentwhere the interface 700 separates the REC 300 and the RE 200. Thecompression subsystem comprises a quantizer (“Quant.”) placed in the RECand respective compression memories (“Compression DB” where DB is shortfor database) in the REC and RE. The compression subsystem could becontrolled by the UPC in the REC. The use of beam direction space asdisclosed above is optionally part of the compression subsystem.

An embodiment of the quantizer of the compression subsystem will now bedisclosed. In general terms, the quantizer can apply reduction of wordwidths, have variable length lists of coefficients and/or apply othercompression techniques. The beamforming weights are applied per OFDMsymbol. A first reduction of the data is to use the same beamformingweights for a set of consecutive OFDM symbols (e.g., a set ofconsecutive subcarriers) in the time domain, typically for a completetransmission. A second reduction is to use the same beamforming weightsfor a set of consecutive OFDM symbols in the frequency domain. The RECcould then inform which beamforming weights to use for each Nsubcarriers, and the RE could then perform interpolation for determiningthe beamforming weights of the subcarriers between these N subcarriers.

In some aspects the value of N is dependent on the channel coherence.Thus, the channel estimate can be processed in order for the REC todetermine a value of N that is small enough to give sufficientbeamforming performance. Each value of N will give a certain SNRperformance, so the choice of N can be determined jointly with otherrelated parameters in the link adaptation, such as output power andmodulation and coding scheme (MCS).

An embodiment of the compression memories of the compression subsystemwill now be disclosed. In order to reduce the load of the interfacebetween the REC and the RE is for to the REC is to send differentialinformation of the beamforming weights rather than a complete set of(quantized) beamforming weights to the RE. Two sources of baseinformation on which the differential information can be based areprevious transmissions of beamforming weights between the REC and the REand beamforming weights determined internally in the RE. Previoustransmissions of beamforming weights between the REC and the RE caneither be from the last transmission (i.e., recent-most used beamformingweights), or as a continuous incremental refinement of beamformingweights. For continuous incremental refinement of beamforming weights,beamforming weights are first transmitted with a coarse resolution andthen more refined, e.g. first using a large value N and then withincrementally smaller values of N. In terms of beamforming weightsdetermined internally in the RE, the RE could be configured to determinethe beamforming weights from its locally stored channel estimate. In thecase that the REC is satisfied (e.g., the RE's assumption of single-usertransmission is correct; one example where the REC is not satisfied iswhen it has received additional information (e.g. about interference)that it wants to use to create better beamforming weights) with thebeamforming weights determined by the RE (e.g. as optimized forsingle-user operation), the REC can indicate this to the RE, thusrequiring less signaling on the interface between the REC and the REthan if beamforming weight information is transmitted. This allows theREC to only send beamforming weights for terminal devices whichbeamforming weights have by the REC been modified (e.g. as optimized formulti-user operation).

An advantage of using the herein disclosed compression memories is thata communications system with stationary terminal devices will have verylittle signaling relating to the beamforming weights over the interfacebetween the REC and the RE since such stationary terminal devices coulduse the same beamforming weights for two or more consecutivetransmissions.

There are different ways of providing the differential information.Examples relating thereto will be provided next. A first example is toprovide additive differential information whereby differentialbeamforming weights are added to the stored beamforming weights. Asecond example is to provide interpolating differential informationwhereby complementary beamforming weights, e.g. in frequency domain, aresent in order to improve the resolution (of beamforming weights havingbeen sent with lower value of N) of the beamforming weights. A secondexample is to provide multiplicative differential information wherebysending a beam form to multiply the beamforming weights with indirection space. Assuming that the beamforming weights are representedas beamforming weight vectors, then each element of the beamformingweight vector corresponds to one direction. Setting one of thoseelements to zero (by multiply with zero) will create a beam pattern witha null in that direction. This can be very efficient to express anulling, i.e. setting a restriction on a transmission.

The transmission of information over the interface between the REC andthe RE in the UL generally is based on the same features as for the DL,but with information relating to channel estimates being transferred(instead of information relating to beamforming weights).

The (S)RS channel estimation function is configured to set a suitablevalue of N, and a suitable quatization. The UPC can, ahead of ameasurement, state the maximum amount to data to send, not to overloadthe interface between the REC and the RE. One way is for the UPC in theREC to provide the RE with a value of N and where the RE then executes.

Particular aspects of efficient selection of UL beams will now bedisclosed in more detail.

It can here be assumed that the UL beams are selected based on thechannel state information. Selecting as a few beams as possible couldreduce the bit rate on the interface between the REC and the RE. At thesame time, more beams allow for more energy to be received and bettersuppression of interferers.

The more terminal devices that are scheduled together and the moreangular spread of the beams needed to reach the terminal devices, themore beams need to be selected in order to reach good demodulationperformance. Also the types of beams used (such as beam widths andenergy per beam) will affect the number of beams needed. Beams withbeamforming weights determined according to SVD (so-called SVD-beams)will require fewer selected beams than beams with beamforming weightsdetermined according to a DFT (so-called DFT-beams) but could requiremore computational resources to compute. Hence there is a tradeoffbetween reduction of bitrate on the interface between the REC and the REand processing complexity of the beam selection. DTF-beams imply that afixed set of beams that evenly cover the whole spatial view seen fromthe RE is used. The DTF-beams can be spread out one-dimensionally(either spread out vertically or horizontally) or they can be spread outtwo-dimensionally (spread out both vertically and horizontally). DFT isone example of creating fixed beams. As understood by the person skilledin the art other methods for creating fixed beams, optionally includinguneven spread of the beams, are equally applicable. SVD-beams imply thatthe set of beams are dynamically decided depending on the receivedsignals from the desired terminal devices and optionally also dependenton received signals from the interfering terminal devices. As understoodby the person skilled in the art other methods for creating dynamicbeams are equally applicable.

The selection of beams can be based on channel estimates of referencesymbol signals, or on channel estimates of demodulation referencesignals (DMRS) embedded in an LTE physical uplink shared channel(PUSCH).

The selection of beams can be performed for each resource block, or forgroups of resource blocks, or even with one common selection for thewhole carrier bandwidth. The selection of beams can be performed withone single, common, selection for the whole carrier bandwidth, since thebeams generally correspond to physical directions and even though thephase of the radio propagation is frequency dependent, the physicaldirections are not.

If multiple terminal devices are scheduled in the same resource blocks,and the RE is connected to one single REC, the selections can be made asthe union of the beams needed for each terminal device. If, for example,three beams are selected for a first terminal device and three beams areselected for a second terminal device and one of the beams is common forthe first terminal device and the second terminal device, then only fivebeams need to be transferred from the RE to the REC. If, on the otherhand, the RE is connected to two RECs, and the first terminal device ishandled by one REC and the second terminal device is handled by anotherREC, then three beams need to be sent to each REC.

According to some aspects the maximum number of beams that can beselected is controlled by the REC. The information about how many beamsthat can be selected are then provided by the REC to the RE over theinterface. This information can be expressed in different ways.According to a first example the information specifies the maximumnumber of beams selected per terminal device. According to a secondexample the information specifies the maximum number of beams selectedin total. According to a third example the information specifies acombined restriction of both the maximum number of beams selected perterminal device and the maximum number of beams selected in total. Giventhese limitations, the RE will decide how many beams that should beselected per terminal device. This can be done by the RE comparing thesignal quality for the terminal devices in each of the beams, and selectbeams with the given limitations. In additions to the limitations givenby the REC, the RE could also need to make the selection such that eachterminal gets at least M≥1 number of beams selected.

FIG. 14 schematically illustrates, in terms of a number of functionalunits, the components of an RE according to an embodiment. Processingcircuitry 210 is provided using any combination of one or more of asuitable central processing unit (CPU), multiprocessor, microcontroller,digital signal processor (DSP), etc., capable of executing softwareinstructions stored in a computer program product 1810 a (as in FIG.18), e.g. in the form of a storage medium 230. The processing circuitry210 may further be provided as at least one application specificintegrated circuit (ASIC), or field programmable gate array (FPGA).

Particularly, the processing circuitry 210 is configured to cause the REto perform a set of operations, or steps, S102-S108, S302-S312, asdisclosed above. For example, the storage medium 230 may store the setof operations, and the processing circuitry 210 may be configured toretrieve the set of operations from the storage medium 230 to cause theRE to perform the set of operations. The set of operations may beprovided as a set of executable instructions. Thus the processingcircuitry 210 is thereby arranged to execute methods as hereindisclosed.

The storage medium 230 may also comprise persistent storage, which, forexample, can be any single one or combination of magnetic memory,optical memory, solid state memory or even remotely mounted memory.

The RE may further comprise a communications interface 220 forcommunications at least with the REC and the terminal devices. As suchthe communications interface 220 may comprise one or more transmittersand receivers, comprising analogue and digital components.

The processing circuitry 210 controls the general operation of the REe.g. by sending data and control signals to the communications interface220 and the storage medium 230, by receiving data and reports from thecommunications interface 220, and by retrieving data and instructionsfrom the storage medium 230. Other components, as well as the relatedfunctionality, of the RE are omitted in order not to obscure theconcepts presented herein.

FIG. 15 schematically illustrates, in terms of a number of functionalmodules, the components of an RE 200 according to an embodiment.According to some aspects the RE 200 comprises an obtain module 210 aconfigured to perform step S102, an obtain module 210 b configured toperform step S104, a (optional) transform module 210C configured toperform step S106, and an apply module 210 d configured to perform stepS108. According to some aspects the RE 200 comprises an obtain module210 e configured to perform step S302, a transform module 210 ofconfigured to perform step S304, a provide module 210 g configured toperform step S306, an (optional) obtain module 210 h configured toperform step S308, a (optional) transform module 210 i configured toperform step S310, and an (optional) apply module 210 j configured toperform step S312.

In general terms, each functional module 210 a-210 j may be implementedin hardware or in software. Preferably, one or more or all functionalmodules 210 a-210 j may be implemented by the processing circuitry 210,possibly in cooperation with functional units 220 and/or 230. Theprocessing circuitry 210 may thus be arranged to from the storage medium230 fetch instructions as provided by a functional module 210 a-210 jand to execute these instructions, thereby performing any steps of theRE as disclosed herein.

FIG. 16 schematically illustrates, in terms of a number of functionalunits, the components of an REC according to an embodiment. Processingcircuitry 310 is provided using any combination of one or more of asuitable central processing unit (CPU), multiprocessor, microcontroller,digital signal processor (DSP), etc., capable of executing softwareinstructions stored in a computer program product 1810 b (as in FIG.18), e.g. in the form of a storage medium 330. The processing circuitry310 may further be provided as at least one application specificintegrated circuit (ASIC), or field programmable gate array (FPGA).

Particularly, the processing circuitry 310 is configured to cause theREC to perform a set of operations, or steps, S202-S208, S402-S408, asdisclosed above. For example, the storage medium 330 may store the setof operations, and the processing circuitry 310 may be configured toretrieve the set of operations from the storage medium 330 to cause theREC to perform the set of operations. The set of operations may beprovided as a set of executable instructions. Thus the processingcircuitry 310 is thereby arranged to execute methods as hereindisclosed.

The storage medium 330 may also comprise persistent storage, which, forexample, can be any single one or combination of magnetic memory,optical memory, solid state memory or even remotely mounted memory.

The REC may further comprise a communications interface 320 forcommunications at least with the RE. As such the communicationsinterface 320 may comprise one or more transmitters and receivers,comprising analogue and digital components.

The processing circuitry 310 controls the general operation of the RECe.g. by sending data and control signals to the communications interface320 and the storage medium 330, by receiving data and reports from thecommunications interface 320, and by retrieving data and instructionsfrom the storage medium 330. Other components, as well as the relatedfunctionality, of the REC are omitted in order not to obscure theconcepts presented herein.

FIG. 17 schematically illustrates, in terms of a number of functionalmodules, the components of an REC according to an embodiment. Accordingto some aspects the REC 300 comprises an obtain module 310 a configuredto perform step S302, a transform module 310 b configured to performstep S304, a provide module 210C configured to perform step S306, and a(optional) provide module 210 d configured to perform step S308.According to some aspects the REC 300 comprises an obtain module 310 econfigured to perform step S402, an (option) obtain module 210 fconfigured to perform step S404, a determine module 310 g configured toperform step S406, and a provide module 310 h configured to perform stepS408.

In general terms, each functional module 310 a-310 h may be implementedin hardware or in software. Preferably, one or more or all functionalmodules 310 a-310 h may be implemented by the processing circuitry 310,possibly in cooperation with functional units 320 and/or 330. Theprocessing circuitry 310 may thus be arranged to from the storage medium330 fetch instructions as provided by a functional module 310 a-310 hand to execute these instructions, thereby performing any steps of theREC as disclosed herein.

The RE and REC may be provided as standalone devices or as a part of atleast one further device. For example, as disclosed above the RE and RECmay be provided in an access node. Alternatively, functionality of theRE and the REC may be distributed between at least two devices, ornodes.

Thus, a first portion of the instructions performed by the RE or REC maybe executed in a first device, and a second portion of the of theinstructions performed by the RE or REC may be executed in a seconddevice; the herein disclosed embodiments are not limited to anyparticular number of devices on which the instructions performed by theRE or REC may be executed.

Hence, the methods according to the herein disclosed embodiments aresuitable to be performed by an RE or REC residing in a cloudcomputational environment. Therefore, although a single processingcircuitry 210, 310 is illustrated in FIGS. 14 and 16 the processingcircuitry 210, 310 may be distributed among a plurality of devices, ornodes. The same applies to the functional modules 210 a-210 j, 310 a-310h of FIGS. 15 and 17 and the computer programs 1820 a, 1820 b, 1820 c,1820 d of FIG. 18 (see below).

FIG. 18 shows one example of a computer program product 1810 a, 1810 b,1810 c, 1810 d comprising computer readable means 1830. On this computerreadable means 1830, a computer program 1820 a, 1820 c can be stored,which computer program 1820 a, 1820 c can cause the processing circuitry210 and thereto operatively coupled entities and devices, such as thecommunications interface 220 and the storage medium 230, to executemethods according to embodiments described herein. The computer program1820 a, 1820 c and/or computer program product 1810 a, 1820 c may thusprovide means for performing any steps of the RE as herein disclosed. Onthis computer readable means 1830, a computer program 1820 b, 1820 d canbe stored, which computer program 1820 b, 1820 d can cause theprocessing circuitry 310 and thereto operatively coupled entities anddevices, such as the communications interface 320 and the storage medium330, to execute methods according to embodiments described herein. Thecomputer program 1820 b, 1820 d and/or computer program product 1810 b,1810 d may thus provide means for performing any steps of the REC asherein disclosed.

In the example of FIG. 18, the computer program product 1810 a, 1810 b,1810 c, 1810 d is illustrated as an optical disc, such as a CD (compactdisc) or a DVD (digital versatile disc) or a Blu-Ray disc. The computerprogram product 1810 a, 1810 b, 1810 c, 1810 d could also be embodied asa memory, such as a random access memory (RAM), a read-only memory(ROM), an erasable programmable read-only memory (EPROM), or anelectrically erasable programmable read-only memory (EEPROM) and moreparticularly as a non-volatile storage medium of a device in an externalmemory such as a USB (Universal Serial Bus) memory or a Flash memory,such as a compact Flash memory. Thus, while the computer program 1820 a,1820 b, 1820 c, 1820 d is here schematically shown as a track on thedepicted optical disk, the computer program 1820 a, 1820 b, 1820 c, 1820d can be stored in any way which is suitable for the computer programproduct 1810 a, 1810 b, 1810 c, 1810 d.

The inventive concept has mainly been described above with reference toa few embodiments. However, as is readily appreciated by a personskilled in the art, other embodiments than the ones disclosed above areequally possible within the scope of the inventive concept, as definedby the appended claims. For example, although the embodiments mainlyhave been described in a time division duplex (TDD) context, at leastsome of the embodiments are also applicable for frequency divisionduplex (FDD). One difference in FDD compared to TDD is that the ULmeasurements cannot for sure be used for DL, due to the differentfrequencies UL and DL. In FDD the terminal device sends informationabout what beam direction the terminal device deems is best (from araster of predetermined beams that the access node is repeatedlytransmitting, i.e. a “code book”). In this case, the REC may need toprovide beamforming weights to the RE (thus defining the externalinformation).

1-40. (canceled)
 41. A radio equipment (RE) of an access node, the REconfigured for obtaining information for determining beamforming weightsfor terminal devices, the RE having an interface to a radio equipmentcontroller (REC) of the access node and comprising processing circuitry,wherein the processing circuitry is configured to cause the RE to:obtain beamforming information per direction from the REC over theinterface; transform the beamforming information per direction tobeamforming information per antenna, the beamforming information perantenna representing the beamforming weights; and apply the beamformingweights.
 42. The RE according to claim 41, wherein the beamformingweights are applied at antennas of the RE.
 43. The RE according to claim41, wherein the beamforming information per antenna is associated with afirst dimensionality, and wherein the beamforming information perdirection is associated with a second dimensionality that is smallerthan the first dimensionality.
 44. The RE according to claim 41, whereinthe beamforming information per direction is obtained as a linearcombination of predetermined beamforming weights per direction.
 45. TheRE according to claim 41, wherein the beamforming information istransformed using a Discrete Fourier Transform (DFT).
 46. The REaccording to claim 41, wherein the processing circuitry is configured tocause the RE to: obtain information appointing fixed beam directionsfrom the REC over the interface, and wherein the beamforming informationper direction is transformed to beamforming information per antenna onlyfor the appointed beam directions.
 47. A radio equipment controller(REC) of an access node, the REC configured for providing informationfor determining beamforming weights for terminal devices, the REC havingan interface to a radio equipment (RE) of the access node and comprisingprocessing circuitry, wherein the processing circuitry is configured tocause the REC to: obtain beamforming information per antenna, thebeamforming information per antenna representing the beamformingweights; transform the beamforming information per antenna tobeamforming information per direction; and provide the beamforminginformation per direction to the RE over the interface.
 48. The RECaccording to claim 47, wherein the beamforming information per antennais associated with a first dimensionality, and wherein the beamforminginformation per direction is associated with a second dimensionalitythat is smaller than the first dimensionality.
 49. The REC according toclaim 47, wherein only the beamforming information per direction havinga signal quality measure above a threshold is provided to the RE overthe interface.
 50. The REC according to claim 47, wherein thebeamforming information is transformed using a Discrete FourierTransform (DFT).
 51. The REC according to claim 47, wherein theprocessing circuitry causes the REC to: provide information to the REover the interface appointing which fixed beam directions to use whentransforming the beamforming information per direction to beamforminginformation per antenna.
 52. The REC according to claim 47, wherein thebeamforming information per antenna is obtained from at least one of theterminal devices.
 53. A radio equipment (RE) of an access node, the REconfigured for providing information for determining beamforming weightsfor terminal devices, the RE having an interface to a radio equipmentcontroller (REC) of the access node and comprising processing circuitry,wherein the processing circuitry is configured to cause the RE to:obtain beamforming information per antenna from at least one of theterminal devices, the beamforming information per antenna representingthe beamforming weights; transform the beamforming information perantenna to beamforming information per direction; and provide thebeamforming information per direction to the REC over the interface. 54.The RE according to claim 53, wherein the beamforming information perantenna is associated with a first dimensionality, and wherein thebeamforming information per direction is associated with a seconddimensionality being smaller than the first dimensionality.
 55. The REaccording to claim 53, wherein only the beamforming information perdirection having a signal quality measure above a threshold is providedto the REC over the interface.
 56. The RE according to claim 53, whereinthe beamforming information is transformed using a Discrete FourierTransform (DFT).
 57. The RE according to claim 53, wherein theprocessing circuitry is configured to cause the RE to: obtain updatedbeamforming weights per direction from the REC over the interface;transform the updated beamforming weights per direction to updatedbeamforming weights per antenna; and apply the updated beamformingweights per antenna.
 58. The method according to claim 53, wherein theupdated beamforming weights are applied at antennas of the RE.
 59. Aradio equipment controller (REC) of an access node, the REC configuredfor obtaining information for determining beamforming weights forterminal devices, the REC having an interface to a radio equipment (RE)of the access node and comprising processing circuitry, wherein theprocessing circuitry is configured to cause the REC to: obtainbeamforming information per direction from the RE over the interface;determine the beamforming weights per direction based on the beamforminginformation per direction; and provide the beamforming weights perdirection to the RE over the interface.
 60. The REC according to claim59, wherein only the beamforming information per direction having asignal quality measure above a threshold is used when determining thebeamforming weights per direction.
 61. The REC according to claim 59,further comprising: obtaining channel rank information from the RE overthe interface, and wherein the beamforming weights per direction aredetermined based on the channel rank information.